TORONTO — The Celtics starters were outscored, 77-52, Friday night against the Raptors at Air Canada Centre, and Brandon Bass believes the recent lack of production may be a chemistry issue.

Brad Stevens went with his bench down the stretch as Boston went on a 26-10 run before losing, 105-103, on Amir Johnson’s putback with 7.1 seconds left.
Rajon Rondo
was the only Boston starter to play more than 30 minutes, while the trio of Bass, Kris Humphries, and Avery Bradley combined for just 18 field goal attempts.

Stevens correctly pointed out that the bench was producing. The reserves scored 49 points, including a team-high 20 from Jerryd Bayless. Bass said the bench’s success is a byproduct of less structure.

“When they’re out there, they’re just playing,” Bass said. “Everything is free flowing. With the first group, we have to play to our strengths, man. We got players out there that have to play to their strengths. If you don’t play to your strengths, it’s like your just out there.”

Jeff Green
, who was slowed by a stiff neck in Wednesday’s loss, led Boston’s starters with 16 points. Humphries (plus-4) was the lone starter in positive figures.

When asked if the issue was chemistry, Bass said: “At times, yes. It shows. When we’re successful we have great chemistry. When we’re not, it’s because we don’t. That has to be what it is. It’s not one particular person. Both groups are different. It’s not really an individual that you can point out and say, ‘he’s the reason why.’ It’s just us as a group. We have to better understand our personnel and the game, it will be simple then.”

Emerging threat

Jared Sullinger entered Friday night having scored 51 points and with 28 rebounds in two games against the Raptors, including a 19-point fourth quarter in Boston’s 99-90 loss Wednesday at TD Garden. His performances caught the attention of Toronto coach Dwane Casey.

Sullinger struggled from the field Friday, with 11 points on 4-for-12 shooting, but finished with nine rebounds.

“He is a handful down in the paint,” said Casey, “He is in great shape. He stepped out on the floor now, shooting threes. So really he’s causing problems from inside and out. So that’s something that we have to be prepared for. They put in a couple of new sets for him the other night that caught us by surprise a little bit.

“So it’s up to [Jonas Valanciunas and Chuck Hayes] to stay connected with him and chase him like he’s a small guy because he’s running off pin-downs and off screens like [Avery] Bradley. Against us, his eyes light up.”

Stevens wants consistency from Sullinger but said sparkling games followed by substandard games is a byproduct of inexperience.

“For a really good player, he’s probably had a typical second year,” Stevens said. “So he’s had some real ups and some games that aren’t so good. The biggest thing is being able to do it every single night, every single time out. But he’s had those moments against other teams, too. We need him to play well for us to have a chance to win. He’s probably our best low-post scorer on most nights.”

When asked if Sullinger could play center, Stevens said: “I think he’s got to play the power forward. He’s only about 6-7 or 6-8. He can play the center in the appropriate matchup and to be very effective at the center spot against the best in the league, he needs to be able to stretch the floor consistently but his main position, and the position where we’d like to play him most often, is the power forward.”

No spoiler alerts

With a remaining schedule that includes teams trying to make the playoffs or jockeying for position, the Celtics have an opportunity to play spoiler. Stevens said there has been no discussion about being motivated by the opponent’s agenda. “No, it’s never come up from us and I’ve never heard them talk about it,” Stevens said. “The biggest thing for us is just to try to play well, to build some continuity toward the end of the season and to build some momentum to play the right way, to play good basketball. Motivation would be from playing and trying to get into the playoffs and enhance your seedings. Guys are looking at it more in the standpoint of getting better within what we do.” . . . Rondo mentioned Wednesday he would consider playing with a mask after receiving nine stitches after a collision with Toronto’s Greivis Vasquez,
but he played Friday with no protective gear, just a bandage over the wound and a headband . . . Toronto won the season series for the first time since the 2006-07 season.